CAPTCHA, which stands for a “Completely Automated Public Turing test to tell Computers and Humans Apart,” is, as it name suggests, a way of determining whether a content user is a human or a computer (i.e. automated user). CAPTCHA typically involves having a computer create a test that will be difficult for a computer or automated user to solve but easy for a human user to solve. The user is prompted to answer or solve the test, which may then be graded by the computer. Accordingly, if the user solves the test, the computer presumes that the answer was entered by a human and, thus, that the user is a human. A common type of a known CAPTCHA requires the user to identify letters, numbers, or a combination thereof provided in a distorted image on the computer screen.
CAPTCHA may be used to prevent automated computer programs (e.g., robots) from performing actions, such as accessing or otherwise manipulating the user interfaces of websites, sending out e-mail spam using webmail services (e.g., Gmail, Hotmail, Yahoo!), or posting on blogs or forums, that may harm or otherwise degrade the service, quality, or speed of a given service. At the same time, known CAPTCHA methods may unintentionally prevent human users from performing those same actions when, for example, the CAPTCHA test is difficult for the human user to solve. This may occur when the distorted image is difficult to read or the distorted image includes a word that is unfamiliar to human users. For these reasons, known CAPTCHA tests may frustrate and annoy human users.